The nation's Catholic bishops have another sticky issue on their plates. President Obama has accepted an invitation to deliver the commencement address at the University of Notre Dame in May and to receive the customary honorary degree. It is quite a coup for the nation's most resonantly Catholic university. American Catholics and their bishops should be proud.

But the bishops have a policy that says "Catholic institutions should not honor those who act in defiance of our [Catholic] fundamental moral principles." Upon taking office, Obama lifted Bush administration restrictions on funding for abortions and for embryonic stem cell research, as he had promised to do. Both actions violated fundamental Catholic principles on the protection of human life.

Although the bishops' policy is directed at dissident Catholic politicians such as Sen. Ted Kennedy, Notre Dame is being criticized for putting institutional prestige ahead of moral principle by allowing its graduating class to hear from the president of the United States, who is not a Catholic. And at least some Catholic bishops agree with the critics.

Already, Bishop John D'Arcy, in whose Fort Wayne-South Bend Diocese Notre Dame lies, has announced that he will not attend the president's speech, having failed to persuade the university to withdraw its invitation. Other bishops are likely to join D'Arcy in distancing themselves from the university. In 1992, when Notre Dame conferred its highest honor, the Laetare Medal, on Sen. Daniel Patrick Moynihan, a low-key pro-choice Democrat who opposed "partial birth" abortions, New York's Cardinal John O'Connor flew to South Bend for a meeting of the American bishops at Notre Dame but in protest refused to step on the campus.

I am an alumnus of Notre Dame. I am adamantly pro-life, independent as a voter -- and greatly pleased that Obama has agreed to speak at my alma mater. He joins six other sitting presidents going back to Dwight D. Eisenhower -- including George W. Bush -- who have addressed the university. Politically, I had disagreements with each of them. Yet I never supposed that by granting them the commencement podium the university was signaling its approval of their policies. Neither, now, should the bishops.

On the dais at Notre Dame, Obama will find a familiar face: Harvard Law professor Mary Ann Glendon, Bush's ambassador to the Vatican, who will receive this year's Laetare Medal in part for her peerless defense of human life. It's important that the president hear her message as well as deliver his own. It is equally important that this kind of engagement take place at a university devoted to both faith and reason. Where else but in a university setting should we expect this kind of principled presentation of issues?

No question, Notre Dame will pay a price for doing what a Catholic university can and should do. The Internet is smoking with protests from conservative Catholic bloggers and pro-life Web sites. One of them claims to have collected 206,000 signatures opposing the president's appearance. These pressure groups are aghast that "Our Lady's University" would welcome so resolute an opponent of the church's position on abortion. Some alumni, especially Republicans, are threatening to withhold contributions and bequests. The Vatican is receiving e-mail demanding disciplinary action.

Catholicism is not a sect that shuns the world as evil. As a body, the American hierarchy has usually been both principled and open to political engagement. The bishops have congratulated the new president on his victory and pledged to work with him on issues affecting social and economic justice. Do they now find him morally unfit to speak at a Catholic university?

Obama is not coming to Notre Dame to press a pro-choice agenda but to address issues that affect all American citizens, including Catholics. He will be speaking to students who, like other Americans, gave him a majority of their votes. He will receive an honorary degree because it is the custom, not as a blessing on any of his decisions.

American bishops should remember that it was only a few decades ago that a Catholic was considered unfit for the White House. Do they now believe that a sitting president is unfit to address a Catholic university? It's time the bishops gave a clear and principled response.

The writer is a contributing editor at Newsweek, where he served as religion editor for 38 years.